The EconomistFebruary 15th 2020 Science & technology 692 va and even dental plaque will do. A study
just published by Feliciano Priego-Capote
at University of Cordoba, in Spain, for ex-
ample, shows it is possible to extract much
meaningful information from even a
dried-up drop of sweat—indeed, Dr Priego-
Capote is able to find in dried sweat sub-
stances that are undetectable at the mo-
ment in fresh perspiration.
Such information can reveal a lot. Your
god? Regular exposure to burning incense,
and thus frequent visits to a church that
uses it, will be detectable from the chemi-
cals in the smoke. Not a Christian? Kosher
and halal diets are detectable by the ab-
sence of metabolites from certain food-
stuffs those diets forbid. Your out-of-office
activities? Habits like drinking, smoking
and narcotic use are visible as numerous
chemicals—not merely the active pharma-
ceuticals which produce the relevant high
or low. Your exercise levels? These are
flagged up by lower than normal levels of
things like leucine, glycerol and phenylala-
nine. Your local environment? Breathing in
polluted air has a marked impact on the
profile of your metabolites. Your general
health? Illnesses ranging from Parkinson’s
disease (altered levels of tyrosine and tryp-
tophan) to diabetes (sugars and sphingo-
myelin) leave abundant metabolic traces.
“The day is coming soon”, observes Cecil
Lewis, a molecular anthropologist at Uni-
versity of Oklahoma, who is studying the
matter, “when it will be possible to swab a
person’s desk, steering wheel or phone and
determine a wide range of incredibly priv-
ate things about them.”
Swabbing the decks
In contrast with dna, the use to which
knowledge of metabolites might be put has
little legal restriction. Dr Lewis, and others
like him, worry about the consequences of
this. At the moment, sampling for alcohol
or illegal drug use, say, has to be overt, be-
cause it involves a blood, urine or breath
test. That is true regardless of who is col-
lecting the sample, whether it be the police
or an employer. This also keeps purposes
clear. A firm might feel it has the right to
test employees for drug use, and the law
might support that. But techniques like Dr
Priego-Capote’s make it easier, as Dr Lewis
observes, to sample clandestinely, and
bring a temptation to push back the bound-
aries of what is being searched for. They
would, for example, allow companies to
detect, if they chose to look, such private
matters as whether an employee was tak-
ing antidepressants.
Metabolite data, even the sort obtained
openly, will also be of interest to medical-
insurance companies, who may insist on
the provision of samples as a condition of
the provision of cover. They, too, might
take an interest in matters of diet and exer-
cise, penalising those who do not conformto prescribed healthy regimes.
The police may be tempted to push the
boundaries as well. The fourth amendment
to America’s constitution protects against
unwarranted searches and seizure of evi-
dence. This means it is hard to force some-
one to give a sample. But if obtaining such
merely requires taking a swab of a surface
in a public place—perhaps a keyboard
someone has just used—the amendment is
unlikely to apply.
That is not necessarily wrong, if it
means more criminals are caught and con-
victed. But it needs to be thought about
carefully, because many metabolites are
sticky. Cocaine is a case in point. Studies
have shown that as many as two-thirds of
the dollar bills in circulation in America
carry traces of this substance, which mightthus end up on the fingertips of the inno-
cent, as well as the guilty.
Perversely, this might even help some-
one who really had taken the drug. The law
in many jurisdictions permits employers
to fire employees for unlawful conduct,
even if it happens outside the workplace.
But as Michelle Terry of wks Law in Los An-
geles, observes, given how sticky research
has shown cocaine metabolites to be, it is
hard to guess how the courts would rule if
someone lost their job for testing positive,
yet claimed never knowingly to have
touchedthestuff. 7I
s itapeak,a stutterorjusta brief
pause? Time will tell. But whatever it is,
on February 11th the International Energy
Agency (iea), an intergovernmental
organisation which collects such data,
announced that emissions of carbon
dioxide in 2019 which were related to
energy had remained the same (33.3bn
tonnes) as the previous year’s.
Energy-related emissions, which
include those produced by electricity
generation, heating and transport, ac-
count for more than 70% of the world’s
industrial CO 2 pollution. The stall seems
to have been caused by a decline in coal
use, particularly in rich countries, com-
bined with an increase in the use of
renewable power.
As a result of this the CO 2 -intensity of
electricity generation—a measure of how
much of the gas is emitted per kilowatt-
hour of juice produced—fell by nearly6.5%,to 340 gramsofCO 2 perkilowatt-
hour. It had already been falling, but this
is three times the average for the past
decade. Such declines more than offset
the effect of increased electricity produc-
tion. The average emission-intensity of
power generation in 2019 was “lower
than all but the most efficient gas-fired
power plants”, according to the iea.
This is not the first time energy-
related emissions have plateaued. Be-
tween 2013 and 2016 they hovered around
32.2bn tonnes a year, before rising again
in 2017 as the use of coal to fuel devel-
oping economies increased. This previ-
ous plateau was accompanied by excited
declarations that such emissions had
peaked. Similar comments have been
made this week, perhaps also premature-
ly. In addition to changes in coal use, a
sluggish economy may have played a part
and the data show that milder than usual
weather caused a perceptible drop in
emissions from several countries with
large, carbon-hungry economies.
The news is also tempered by the
latest data from the Amazon rainforest.
This, one of the world’s largest wood-
lands, has acted historically as an ab-
sorbing sponge for CO 2 by removing it
from the atmosphere through photo-
synthesis. Researchers at Brazil’s Nation-
al Institute for Space Research have
shown that a vast part of the south-east
of the Amazon, about one fifth of its area,
has lost its ability to soak up the gas and
is now a net source of emissions into the
atmosphere instead. This land has been
widely deforested, so the result is little
surprise. But it is disappointing.Goodish news
Climate changeEmissions of carbon dioxide related to energy production have stabilised, for nowFlat chance
Energy-relatedCO2emissions, tonnes, bnSource:IEARestoftheworldOECD and the EU2000 05 10 1915403020100Correction: In “No small matter” (February 1st) we
suggested that Charles Lieber’s research at Harvard
was connected with Elon Musk’s brain-machine
interface project. In fact Neuralink, Mr Musk’s firm,
is completely separate from Dr Lieber’s endeavours.